Few large animal models exist to study abdominal aortic aneurysms, but these models are critical to assessing the viability of novel technologies and treatments for human disease. The combination of elastase and a compound called BAPN creates aneurysms that are large and contain sequelae of chronic aneurysmal disease, such as thrombi, dissections, and ruptures. Demonstrating the procedure with me will be Doctors Jolian Dahl and Erik Scott, fellow surgical residents.
Seven days before the surgery, provide 20 to 30 kilogram non-castrated male swine with standard chow supplemented with BAPN given in weight-based dose and mixed in whole milk plain yogurt. On the day of the procedure, confirm an appropriate level of sedation and drape the pig in the standard fashion. Ensure all of the necessary instruments are organized and ready on a sterile draped table.
This includes the instrument tray, micropuncture introducer kit, 025-millimeter Glidewire, saline flushed tested 16-millimeter percutaneous transluminal angioplasty balloon, and connected pressure syringe. Using electrocautery, perform a midline laparotomy to enter the abdominal cavity taking care to stay to the right of the penis and its shaft to avoid injury. Tuck one side of a saline soaked sterile blue towel into the left paracolic gutter, and then use it to cover the bowel to avoid desiccation before displacing the abdominal viscera to the pig's left exposing the retroperitoneum.
While one operator retracts the sigmoid colon and rectum to the left, the other surgeon palpates for the aortic pulse to identify the appropriate site to incise the retroperitoneum. Tent the retroperitoneum and use electrocautery to incise and enter the retroperitoneum, facilitating access to the inferior vena cava and infrarenal abdominal aorta. Circumferentially dissect approximately three centimeters of the aorta at the midpoint between the right renal artery and aortic trifurcation to allow for baseline measurement of the aorta before full dissection causes aortic spasm.
Take care to avoid injury to the right ureter. Once a short segment of the aorta has been exposed, use calipers to measure its diameter. After measurement, complete the circumferential dissection of the entire infrarenal aorta.
Identify the caudal mesenteric artery on the anterior portion of the infrarenal aorta, which usually lies a few centimeters proximal to the aortic trifurcation and dissect.Clamp. And transect this artery. Administer 100 units per kilogram of unfractionated heparin sulfate intravenously.
Use a 018-inch stainless steel wire guide from a micropuncture introducer set to cannulate the caudal mesenteric artery. Serially dilate the artery over the wire first with a 5 French micropuncture introducer, followed by a 7 French dilator. Leaving the 7 French introducer in place, replace the 018-inch wire with a 035-inch guidewire and remove the 7 French dilator, ensuring hemostasis by pinching or placing a finger over the cannulation site.
Advance the 035-inch guidewire until approximately 30 centimeters of wire remains or resistance is encountered. Insert a 16-millimeter percutaneous transluminal angioplasty balloon over the wire into the infrarenal aorta. Once the balloon is inside the aorta, remove the guidewire and place a finger over the wire port of the balloon to prevent hemorrhage.
Inflate the balloon while intermittently measuring the diameter of the dilated aorta with calipers until maximal dilation is approximately 80%greater than the baseline measurement. Deflate and adjust the depth of the balloon catheter before fully inflating to ensure that the dilated segment is at the midpoint of the dissected aorta. Once the desired dilation is achieved, turn the three-way stopcock between the pressure syringe and balloon catheter to off towards the balloon and leave the aorta dilated for 10 minutes.
Replace the guidewire and then deflate and exchange the balloon for 7 French dilator, before removing the wire, and allowing for 10 minutes of reperfusion. Be sure to confirm the aortic pulse distal to the balloon dilated segment. At the end of the reperfusion, identify and clamp the previously dissected lumbar vessels to isolate the infrarenal aorta from systemic circulation to avoid systemic perfusion of the elastase.
Cross clamp the aorta just distal to the renal vessels and proximal to the aortic trifurcation. Potts tourniquet the portion of aorta containing the 7 French dilator just proximal to the cannulation site with a vessel loop. Remove the wire and flush the isolated aortic segment with saline confirming no leakage of fluid.
Connect 500 units of elastase and 8, 000 units of collagenase solution to the introducer. Perfuse the entire 30 milliliters of solution into the isolated aorta under constant manual pressure for 10 minutes. After 10 minutes, irrigate the solution from the aortic lumen with saline.
And remove the introducer. Ligate the caudal mesenteric artery stump or place a 5-0 prolene repair suture if the stump was destroyed. And release the lumbar clamps, the distal clamp and the proximal clamp.
Soak a two-by-five centimeter piece of surgical gauze with 20 milliliters of undiluted elastase and wrap the gauze around the intervened aorta for 10 minutes. After measuring the aorta with a caliper, irrigate the abdomen with saline. Replace the bowel.
And close the fascia, deep dermal layer, and skin in three layers. Then inject 0.2 milligrams per kilogram of long-acting buprenorphine intramuscularly into the left thigh for postoperative analgesia. The combination of the BAPN and surgery providing elastase treatment creates a more robust and reproducible abdominal aortic aneurysm in swine at day 28 compared to animals treated with surgery and elastase alone.
Abdominal aortic aneurysm grows progressively larger as time progresses, and evidence of chronic aneurysmal disease is evident in animals treated with BAPN and surgery with elastase, including intraluminal thrombus and atherosclerosis. Further, histologic evaluation demonstrates a significantly increased elastin fragmentation in BAPN-treated swine abdominal aortic aneurysm than in animals treated with surgery and elastase alone, as well as an increased collagen alteration. The induction of abdominal aortic aneurysms via laparotomy can be daunting for non-surgically trained investigators, and a team effort is required for this model to be successful.
Remember that the sharp instruments used during this procedure can cause actual harm to the operators and to exercise caution when sharp needles or instruments are on the surgical field.
